This application relates to torque wrenches of the click type and, in particular, to click mechanisms for such wrenches.
Click-type torque wrenches derive their name from the fact that they signal the achievement of a predetermined torque level by generating an audible and/or tactile “click.” Such torque wrenches typically have an elongated tubular lever arm coupled at one end to a workpiece-engaging head by a pivot arm which extends into the tube, a handle being provided at the other end of the tube. The click mechanism includes a spring-loaded cam plunger which is slidably disposed within the tube and is biased toward the inner end of the pivot arm, for trapping therebetween a trip block or pawl which is seated in recesses formed in the facing ends of the pivot arm and cam plunger. The spring force, which is adjustable, drives the trip block axially against the inner end of the pivot arm so as to hold the pivot arm in a position aligned substantially coaxially with the tube until the applied torque reaches a level which causes the pivot arm to overcome the spring force and pivot, moving its inner end laterally to tip the trip block, camming the cam plunger rearwardly in the tube and allowing the inner end of the pivot arm to strike the inner surface of the tube, creating the click. When torque is released, the spring drives the parts back to their original positions.
While this arrangement works well, it has created several problems. When the trip block tips, it applies a lateral force against the front end of the cam plunger tending to cause its front end to move laterally more than the rear end, which can cause the front peripheral edge of the cam plunger to create surface galling of the inner surface of the tube as the cam plunger moves axially back and forth. Heretofore, this problem has been overcome by internal surface hardening of the tube through a heat-treating process. However, this heat treating process can cause distortion of the thin-walled tube and can create a significant degree of surface finish degradation. This surface finish damage and physical distortion of the tube then necessitates secondary processing operations to create surface finish and tube straightness, which add cost to the tool.
Furthermore, it has been found that in prior tools the lateral movement of the inner end of the pivot arm to create the click is sometimes sufficient to completely roll over the trip block or pawl so that it does not return to its proper position when torque is released. In order to alleviate this problem it has been necessary in prior designs to add a spacer ring press-fitted onto the end of the pivot arm to restrict the lateral or side-to-side movement of the pivot arm, thereby further adding cost to the tool.